The incidence of SSI in abdominal surgery has been reported to range from 4.8–7.4% in China [9, 10]. In our study, we found a high rate of 29.6% (37/125) following emergency abdominal surgery (EAS) in elderly. Our high rate of SSI may be explained by the fact that a patient with acute bowel obstruction cannot receive sufficient bowel preparation prior to surgery. A meta-analysis has reported that mechanical bowel preparation can decrease the risk for SSI in elective bowel surgery , but this remains a controversial issue. A recent randomized controlled trial of 396 patients undergoing elective colonic surgery showed no difference in SSI and overall morbidity between the mechanical and oral antibiotic bowel preparation group and the no bowel preparation group . However, confirmation of the relationship between the abundance of bacteria in the intestinal lumina and SSI needs to be addressed by more high-quality studies.
E. coli is reported as the most common pathogen causing SSI in abdominal surgery [13, 14]. Similarly, our findings showed that E. coli was the leading pathogen isolated from surgical sites (16/43; 37.2%), with most isolates resistant to third-generation cephalosporins (15/16; 93.8%). Resistance of pathogens isolated from abdominal surgical sites in a multicenter cross-sectional study in China were not available [9, 14]. This is higher than the prevalence (61.1%) of extended-spectrum beta-lactamase (ESBL)-producing E. coli from community-onset bloodstream infections reported in South-West China and associated with older age groups . Golzarri et al also reported that patients colonized by ESBL-producing Enterobacteriaceae (ESBL-PE) were at high risk for SSI .
In our study, ESBL-PE isolated from surgical sites accounted for 72.4% (21/29) and would contribute the higher rate of patients with SSIs. For this reason, cefoxitin was chosen as the prophylactic agent for patients in the latter period of our study. Preoperative cefoxitin had a better efficacy to prevent SSI, but was less significant (SSI rate: cefoxitin vs. others: 15.4% vs. 31.3%, respectively; p = 0.236). Similarly, in a large study by Poeran et al , cephamycins did not demonstrate a better efficacy for SSI prevention compared with non-cephamycins. In another study, it was reported that cefoxitin concentrations were not sufficient in subcutaneous adipose tissue (< 8 mg/mL) at the time of surgical closure in obese patients who received a sleeve gastrectomy . These findings suggest that it would be beneficial to develop a new prophylactic antimicrobial agent or enhance the potency of preoperative cefoxitin to prevent SSI with an appropriate dosage. Positive effect of preoperative surgical antibiotic prophylaxis on SSI have been recommended [19, 20], but the optimal timing is still a subject of debate. In our study, it was difficult to determine the beginning of the actual time of antibiotic administration as this information was not well documented for emergency patients and thus we were unable to assess the optimal timing of preoperative surgical antibiotic prophylaxis.
In this retrospective study, 92.0% (115/125) of patients had a longer (> 48 hours) duration of postoperative prophylactic antibiotic use than recommended (< 24 hours) by the ASHP  and national technical and administrative documents [8, 20], although 32 (86.5%) cases of SSIs were diagnosed before the end of the prophylaxis course. However, it’s hardly alone. Prolonged postoperative antimicrobial prophylaxis focusing on EAS was startling common in many settings during the same time , although it was limited by guideline from Chinese Surgical Society of Chinese Medical Association  and hardly supported/reported in literature in the country. In the multicenter, prospective, cross sectional study , adult patients who underwent EAS in 47 tertiary hospitals in China during 1–2 months from 2018 to 2019, only 3.46% patients were admitted with (less than) one-day perioperative prophylactic antibiotics. In our study and their studies, there was no evidence to show that longer use of postoperative antimicrobial prophylaxis had a protective role for the incidence of SSI and our findings confirm this observation compared with similar reports [6, 9, 14]. According to the WHO guidelines for the prevention of SSI, the panel recommends against the prolongation of surgical antibiotic prophylaxis administration after completion of the procedure for the purpose of preventing SSI . However, there is ongoing controversy on this issue  and more randomized controlled trials are necessary to confirm or not the existence of any benefit of postoperative surgical antibiotic prophylaxis for the prevention of SSI.
We identified a level III surgical incision as an independent risk factor for SSI as it is more exposed to a contaminant and thus a high risk of infection. We observed that the duration (≥ 117 min) of the surgical procedure was related to the occurrence of SSI. Complex procedures are often long and thus the incision and the wound are more exposed to the risk of SSI. Sattar et al  reported that SSIs were more likely in procedures with a duration greater than 90 min and particular attention should be paid to the wounds of patients undergoing a lengthy procedure. The serum albumin level has an important role in the development of SSI, but not well evaluated in elderly patients.. Liang et al  also reported that the rate of low albumin levels was 35.1% in SSI patients. In particular, a low preoperative albumin level (< 35 g/L) was associated with a 2.3-fold increased risk of SSI. In our study, we did not test the preoperative albumin level, but we analyzed the effect of the first day of postoperative albumin on SSI and demonstrated that a level of < 25 g/L was significantly associated with SSI in emergency bowel surgery, potential leading also to tissue edema, a delay of incision recovery and an increase in the risk of SSI. In a prospective cohort study, a decreased concentration of serum albumin ≥ 10 g/L on postoperative days 1 was associated with a threefold increased risk of overall postoperative complications 
WHO recommends that bathing or showering prior to surgery can reduce SSI by decreasing the bacterial load on the skin . However, this is not always possible for emergency patients. We were unable to determine if a history of chronic disease, such as diabetes mellitus, cardiovascular disease or others, had any adverse influence on SSI. However, several observational studies have shown that hyperglycemia was related to SSI  and it would be relatively simple for our surgical teams to comply with the WHO recommendation to control blood glucose to reduce the risk of SSI . No deaths occurred among our patients in the 30 days following emergency surgery. Gomila et al  reported that the overall 30-day mortality caused by organ-space SSI was 8.9% (30/336) in elective colon and rectal surgeries and these findings suggest that more attention should be paid to the prevention of deep SSI to help decrease mortality.
Our study has some limitations. First, this is a single-center study and data collection might be biased and some confounding factors may have been generated due to its retrospective nature, e.g. lack of antimicrobial exposure and previous administration history. Second, it was difficult to determine the beginning of the actual time of antibiotic administration as this information was not well documented for emergency patients. For this reason, we were unable to assess the optimal timing of preoperative surgical antibiotic prophylaxis, although the optimal timing is still a subject of debate . Third, underlying risk factors, such as blood transfusion, hypothermia and preoperative albumin level, were not assessed. Fourth, perioperative management against SSI in this study was not based on evidence-based guidance  and the implementation of a bundle strategy for the prevention and management of SSI was not introduced during the study period [19, 28].